issue with external screen

Hi, I bought a few days ago a surface Pro 3, and then by now I am one of your: P
I write to you as it is since I bought the surface that I have problems with the external monitor and I could not find anyone with the same problem.
When I start the surface connected to the external monitor, one of S2240L, everything you see in the picture as well.
As soon as I unplug the monitor and use the screen surface this does not look good,
precisely the size of text and other elements is not setup correctly (you can see everything very small) if restarting the surface. In fact, as you can see from the picture below, after reboot everything is set up correctly.
you can resolve this problem in any way? Of course, the problem is also in contrast, work with the surface and when I connect it to the PC I have to restart everything else you see great !!

i use only one monitor at a time, i don't extended or duplicated the monitor.
thanks in advance

Does the external monitor look OK now? If so, maybe just leave it like this.

But if you want to just have one screen on, press Windows-logo-key + P then up or down arrow and try switching between "PC screen only" and "Second screen only".

Click to expand...

thanks for the reply. The monitor is a Dell S2240L, I tried what you wrote but unfortunately it does not solve the problem, if i work with the Dell monitor and after unplug this, the surface has the dimension wrong. it is really frustrating having to reboot every time